In-orbit refueling tests begin at International Space Station

Astronauts aboard the International Space Station have begun a series of small …

On March 9, NASA astronauts aboard the International Space Station quietly began learning the space exploration equivalent of how to remove and replace a gas cap. It's the first in a series of small demonstrations that are intended to have big future consequences, an attempt to learn how to refuel a spacecraft in space instead of on the ground. The experiments have been hotly anticipated in the space community.

The Robotic Refueling Mission demonstrations were developed by the SSCO team headed up by Frank Cepollina at the NASA Satellite Servicing Capabilities Office (SSCO), formed in 2009 at NASA Goddard Space Flight Center. The team is known for its previous experience planning and executing five highly successful servicing missions for the Hubble Space Telescope.

The past and future of service

In the forty years since the dangerous repairs due to the loss of Skylab's sun shield in 1973, tools, techniques, robotics and spacesuits have improved immeasurably. We've had plenty of chances to practice. In 1984, astronauts in Space Shuttle Challenger retrieved Solar Max, repaired it, and set it free again. Later in 1984, astronauts in Discovery retrieved two more satellites using Manned Maneuvering Units, and returned them to Earth for repair.

The Hubble repair missions came later, and were so successful that questions arose regarding whether we might try the repair and refueling of satellites that weren't designed to be serviced. What about applying what was learned with Hubble to other missions, including spacecraft in positions much farther from Earth? Just before Hubble's last repair, Congress appropriated $20M in the 2009 budget for Goddard Space Flight Center to go further.

In March 2010, Goddard's SSCO held the International Workshop on On-Orbit Satellite Servicing to begin a discussion on what was needed by industry. The SSCO issued a Satellite Servicing Project Report later in the year, and has since designed the Robotic Refueling Mission and ground test-beds.

The unassuming Robotic Refueling Mission features a large box "about the size of a washing machine," according to the SSCO website, with "protective thermal blankets, caps, valves, simulated fuel, and other servicing-related spacecraft components" designed to teach humans the various aspects of refueling in space. SSCO's current work will be important to satellite operators, but it may be even more important to future historians and the rest of humanity—once we get technology that works, we tend to stick with it.

For satellite repair and refueling, astronauts will pull back the satellites' thermal blankets and dig their way through various obstacles to the fuel valves. Today's satellites aren't designed to be repaired or refueled because it has been thought to be unfeasible. There isn't any question of value, though; billions of dollars have been paid out in insurance claims, and some satellites have died with their transmitters stuck at full power as they floated out of their orbits.

Servicing constellations of similar satellites in similar orbits would be most cost-effective, but once the infrastructure is established, the cost of getting to most satellites should be quite low. Many repairs would be automated or controlled by humans either on Earth or in orbit. The refueling or repair vehicles would match orbits, rendezvous, service, and return for more propellant. It's the "return for more propellant" part that brings us to on-orbit propellant depots.

An early concept drawing for an orbiting propellant depot servicing a nuclear shuttle.

Propellant Depots

Imagine that you're about to begin a trip from New York to Los Angeles and back in a world with only one gas station, in Manhattan. You go shopping for a car that gets 30 miles per gallon with a 200-gallon gas tank. 200 gallons weighs 1200 pounds, so you quickly realize you're going to end up with something bigger. But pickups don't get good mileage, so you need a bigger tank... By the time you're done, you have a 2-ton truck that gets 11 miles per gallon and is mostly fuel tank.

With that picture in your mind, imagine that you now need to travel 100 times as far, and most of the trip is straight uphill. Welcome to the challenges of space travel.

For spacecraft, which use a variety of fuels and oxidizers, the gas station equivalent is a propellant depot. These are an enabling and potentially disruptive technology for spaceflight. Depots have been discussed since the 1960s, but for the first time since then, the discussions are becoming serious.

Propellant tanks can be flown weeks or months ahead of time to wherever they need to be, in some cases by slow, low-cost tugs. If a depot was placed at the Space Station, for instance, space travelers could depart Earth any time the weather was good, then wait at the station for Earth and Mars to swing around to the right positions. The travelers might go to another depot just beyond the Moon, and on to Mars, where more propellant would already be waiting for the return trip.

They could also set off a self-sustaining cycle. Satellite repairs beget propellant depots. Propellant depots beget more satellite repairs plus more long-term hardware in space. More propellant depots beget more space exploration and more infrastructure.

A robot like this one next to Astronaut Cady Coleman might be sufficient to handle refueling duties.

Robonauts And Astronauts

These very early SSCO experiments are intended to provide a direction for future operations. The Robotic Refueling Mission calls for EVRs combined with Dextre, the ISS' dextrous robotic arm. Future efforts may allow the astronauts to stay inside the station and instead use Robonauts mounted on the end of the arm. For now, the majority of the work will concentrate on small tasks involving non-cryogenic fuels common in the satellite industry. After those experiments are concluded in 2013, RRM Phase 2 will go up aboard a Japanese HTV, with replacement boards that demonstrate mating of connectors and a conceptual cryo refuel. Further tasks are still in the planning stages.

According to Dr. Edward Cheung, the team's electrical lead engineer, "At some point, our servicing vehicle will be designed to not only deliver fuel with a hose, but be able to fill up our own tanks with our hose, and thereby extend our own life. So this part of the technology relates directly to being able to get fuel from a passive tanker." Dr. Cheung stressed that right now the work "is conceptual and for study purposes—we do not have approval for an actual mission."

For now, these demonstrations will prepare us for the time when necessity demands that we do more. But many who are watching the technology develop hope that the first depot will launch based on what the RRM and its follow-ons engender. Regardless, there isn't any doubt that something very significant is taking shape in orbit from a task that, on first examination, seems very common.

*This* will unlock private participation in space. Bulk fuel and consumables can be lifted by very simple and cheap launchers subjected to market pressures, and human launching, which is a lot more complex, can be left to the specialists.

Hmmm. So lets say I somehow find myself in orbit and I need to fill up my tank how much would this run me? For simplicity's sake I'll assume I'm flying an RV. A rough estimate of the cost of material launched into orbit by a Soyuz spacecraft is about $12,500 per pound. A gallon of gas/diesel weighs in at 7.1 pounds making the cost of orbiting a gallon of gas about $88,750. Say the average price of a gallon of gas here in the US is $4.00 a gallon and we have gas prices of $355,00 per gallon. The average Winnebago as we know has an 80 gallon tank, so to fill said tank, I can expect to pay $28,400,000 at the pump according to my back of the envelope calculation.

Heak, I suppose if I was flying through space in an RV I'd be broke too.....

I think there is merit to fuel depots, in that there may be a market that would support such technology in terms of extending the life of satellites, and there may even be a use for it in longer-term human voyages. However, what I don't understand is how a fuel-depot is a useful component for NASA to fund right now. In fact, stepping back a bit at the possible risk of derailing this conversation... NASA in the post-Apollo era, is a really program in search of a vision. Or, put another way... the big-picture vision that I see amounts to a 40-year mission to prepare to do something else big after Apollo. I suppose the current programs being funded do fit within the stated vision ("To reach for new heights and reveal the unknown so that what we do and learn will benefit all humankind."), which is only true because the stated vision is utterly incoherent when compared to Kennedy's Vision. Kennedy's vision... "To put a man on the moon and return him safely to Earth before the end of the 1960", was a clear vision that aligned resources, and created stepping stones. Likewise, SpaceX wants to build an interchangeable platform to service LEO, Luna, and Mars. It's a coherent strategy, and makes sense like Apollo did. The current NASA vision makes no sense, fails to align programs, and results in an incoherent approach that only serves to continue preparing to do something big. Instead, NASA (or another agency) should establish a vision that aligns programs and funding that get's us somewhere, by a certain point in time... and supports the original research and technologies necessary that serve that vision. As to what that vision could be... "A manned mission to Mars within the decade" would count. Likewise, a vision of "Establishing a means to provide a step-change in terms of reducing travel times within the solar system within 8 years", etc. It would revolutionize NASA, realign and eliminate many programs, and move us forward in an arrow, instead of throwing funds at a bunch of programs and seeing what sticks.

What this really is, is just another LEO excuse to delay real human exploration.

Absolutely exciting stuff! When they get this going, it will open up a lot of opportunities for human spaceflight, among other things. This is huge!

No, not by much. As long as we use chemical fuel we won't get very far.

Don't focus on the limitations of chemical rockets. Think instead of the potential for an increased presence in space. Currently all space infrastructure is disposable (aside from the ISS). Once a satellite breaks down, or runs out of fuel that's it. Having even semipermanent propellant depots increase satellite life, and reduces launch costs, since you don't need to store enough fuel for its entire lifetime. This allows for an increase in capability since fuel weight can be replaced with extra components.

This idea can be extended further. With satellites operating longer, it would make sense to put replacement parts in orbit. An orbital warehouse stocked with extra solar panels and circuit boards would reduce the long term operational costs (don't have to replace satellites as often). Launch parts in bulk when convent, and pull the parts when needed.

The presence of orbital depots and warehouses, plus the associated bulk launch services, enable the establishment of small orbital factories. Pharmaceuticals and semi-conducting crystals are excellent candidates for early orbital industry. Both have relatively cheap and light components available in bulk, and the resultant products are of high value.

Obviously this is not guaranteed to happen. Someone needs to recognize the opportunities and act on them. Still, expanding our current space infrastructure increases our ability to maintain and increase our presence in space. Yes, chemical rockets limit what we can do now, but the greater our presence in space the more people will work on improving space technology.

Hmmm. So lets say I somehow find myself in orbit and I need to fill up my tank how much would this run me? For simplicity's sake I'll assume I'm flying an RV. A rough estimate of the cost of material launched into orbit by a Soyuz spacecraft is about $12,500 per pound. A gallon of gas/diesel weighs in at 7.1 pounds making the cost of orbiting a gallon of gas about $88,750. Say the average price of a gallon of gas here in the US is $4.00 a gallon and we have gas prices of $355,00 per gallon. The average Winnebago as we know has an 80 gallon tank, so to fill said tank, I can expect to pay $28,400,000 at the pump according to my back of the envelope calculation.

Heak, I suppose if I was flying through space in an RV I'd be broke too.....

I think there is merit to fuel depots, in that there may be a market that would support such technology in terms of extending the life of satellites, and there may even be a use for it in longer-term human voyages. However, what I don't understand is how a fuel-depot is a useful component for NASA to fund right now.

That's why this is just a test/experiment, not a full blown depot.

Quote:

What this really is, is just another LEO excuse to delay real human exploration.

I can't believe after almost fifty years of manned spaceflight we are only developing this capability now. Someone was asleep at the wheel!

Hm. It's really not that hard to understand once you think of it in terms of scale. Historically, exploration has gone in fits and starts, not a steady linear progression. After thousands of years of manned seafaring, even in the Age of Exploration groundbreaking sea voyages could be 50 years apart.

We are too used to the short, recent history of technological change. It's a nice exponential Moore's Law type of curve, but this curve meets its match when lined up against the curve of manned space flight. Getting to the moon was like when you first crossed the street as a kid. It's a long way from that to going on an interstate road trip by yourself. On the scale of space flight, getting to the moon is practically no distance at all.

And yet we paid a king's ransom of US dollars to get that short distance.

It was not a matter of someone being asleep at the wheel. They just couldn't get funded anymore. In an age where the loudest voices in politics are screaming to tear down government and cut all programs, good luck getting funding at the scale necessary to keep a crew alive for the entire duration of a round-trip interplanetary mission.

We won't be stopped from pushing further into space. But it will always be driven with the economy with the most spare cash, whether that is the US of the 1960s, China, or a private company with more efficient operations than any government. And it may take decades between major space achievements, because it may take decades for a single entity to amass enough funds and the technology needed for the next big leap. Because once you get past the moon, it doesn't just get a little bit harder and more expensive, it gets a lot harder and a lot more expensive...yet the most powerful nation on Earth could barely afford to get to the moon.

I thought most orbiting satellites are solar energy and battery based? Why would they need propellants? I get that moon and mars trips require them but why satellites? If mainly satellites, what about a solar panel powered battery depot?

Is there any way to use electric power to move in space? Imagine the cost benefits if you can space several solar panel based permanent and free depots to get to mars and back.

All satellites gradually spiral in towards the earth, which means they need thrusters to maintain their orbits. Also, because of imperfections in Earth's gravitational field, they end up being forced to rotate slightly, and so need other little thrusters to make sure their antennas and sensors are pointed the correct direction. There are electricity-based ways to maintain your orientation, but all changes in linear momentum (to my physics 101 knowledge) require you to throw mass in the other direction. Rotations can be counteracted by momentum wheels, but eventually the wheels end up spinning too fast and you need to burn off the angular momentum by firing a thruster.

The trouble with fuel depots is that getting from there to the satellite means changing orbit and inclination and this is *expensive* fuel-wise. Often more expensive than landing and launching into the right orbit. It might make sense for GSO satellites, but nothing else. Additionally you can store only storable fuels (that is, nothing that requires cooling) and these fuels are totally the wrong ones for Mars missions and similar.

Fuel depots have some merits for very specialized applications, but in the big picture they won't change very much.

The trouble with fuel depots is that getting from there to the satellite means changing orbit and inclination and this is *expensive* fuel-wise. Often more expensive than landing and launching into the right orbit. It might make sense for GSO satellites, but nothing else. Additionally you can store only storable fuels (that is, nothing that requires cooling) and these fuels are totally the wrong ones for Mars missions and similar.

Fuel depots have some merits for very specialized applications, but in the big picture they won't change very much.

Making launches cheaper in the first place is much more important.

Uh, there's not much we can do to change basic physics. The fuel has to get up there, and there's not much we can do to make that cheaper.

I think there is merit to fuel depots, in that there may be a market that would support such technology in terms of extending the life of satellites, and there may even be a use for it in longer-term human voyages. However, what I don't understand is how a fuel-depot is a useful component for NASA to fund right now.[snip]Kennedy's vision... "To put a man on the moon and return him safely to Earth before the end of the 1960", was a clear vision that aligned resources, and created stepping stones[snip]What this really is, is just another LEO excuse to delay real human exploration.

I don't agree. If you look closely at what happened during and after Apollo, you'll find that practical, pragmatic space exploration ended. During Apollo the Space Belt states grew accustomed to the money, certainly, and that's been destructive. Post-Apollo, a dysfunction crept into the system whereby NASA was hamstrung by Congress for forty solid years. The Flexible Path goals in place right now more closely resemble the pragmatic plans for exploring the solar system from the 1960's than any space program in between. Many who follow the program's history consider this program to be potentially the best program ever, potentially because there's a battle going on between the pragmatism of developing the necessary tools (like orbital refueling) first and the hurricane of money that flies around the Space Belt building projects that were designed for politics and not for exploration.

This effort and a lot of other quiet projects within NASA right now are an attempt to finally get out of LEO. The project in this article is a box with a few boards on it, isn't it? You wouldn't recognize it as a building block to get out of LEO because it hasn't been billed that way until this article, frankly, and there are at least a dozen other groups doing the same thing right now, *trying to fly under the radar*.

So I believe you might have it exactly backwards: the big "visionary" projects are the ones designed to make us to think someone's visionary, and the little projects, the quiet and cheap demonstrations, are the ones that have the best chance of sneaking past Congress and allowing NASA to do their job of getting us to the other planets. Each successive president that comes to office has new priorities, and combined with the congressional priority to funnel money to each representative's district, very little can be done at NASA unless it's done quietly. In this case, the work is being funded as a precursor to commercial satellite repair, and, really, who can argue with that? Don't look for progress in big programs, because they get canceled every few years.

So they're still using liquid fuel? Isn't solid fuel comes easier on refueling, storage and less weight to deal with than liquid fuel? I suppose one pound of solid fuel out last one pound of liquid fuel.

The trouble with fuel depots is that getting from there to the satellite means changing orbit and inclination and this is *expensive* fuel-wise. Often more expensive than landing and launching into the right orbit. It might make sense for GSO satellites, but nothing else. Additionally you can store only storable fuels (that is, nothing that requires cooling) and these fuels are totally the wrong ones for Mars missions and similar.

Fuel depots have some merits for very specialized applications, but in the big picture they won't change very much.

Making launches cheaper in the first place is much more important.

Orbital fuel depots are absolutely capable of storing cryogenic fuels, and they've been a part of advanced planning since the early 1960's. The vacuum of space is nothing if not the best Thermos bottle ever. All one needs is an umbrella to keep off the sun.

So they're still using liquid fuel? Isn't solid fuel comes easier on refueling, storage and less weight to deal with than liquid fuel? I suppose one pound of solid fuel out last one pound of liquid fuel.

Solid fuel has its own problems. Primarily, you can't use it to power multiple rockets at once. Solid fuel is essentially a one-way burn. So each thruster on a satellite would need its own solid fuel source... and that introduces balance problems if one depletes faster than the rest, altering the satellite's center of gravity. And, as in the name, it's basically a solid which makes refueling more difficult.

So they're still using liquid fuel? Isn't solid fuel comes easier on refueling, storage and less weight to deal with than liquid fuel? I suppose one pound of solid fuel out last one pound of liquid fuel.

Solid fuel has its own problems. Primarily, you can't use it to power multiple rockets at once. Solid fuel is essentially a one-way burn. So each thruster on a satellite would need its own solid fuel source... and that introduces balance problems if one depletes faster than the rest, altering the satellite's center of gravity. And, as in the name, it's basically a solid which makes refueling more difficult.

It's also one time use IIRC and satellites need to correct their orbits a lot more often than only once in their lifetime (and even if it was once it would be one burn and that's it). Can't really shut off the solid fuel thruster.

Absolutely exciting stuff! When they get this going, it will open up a lot of opportunities for human spaceflight, among other things. This is huge!

No, not by much. As long as we use chemical fuel we won't get very far.

I would agree that so long as we're burning that chemical fuel then we're always going to be limited. However, even more advanced propulsion options (e.g. ion drives) are still going to require some sort of propellant, even if that's just inert gas. So on-orbit refuelling will still be huge.

Hmmm. So lets say I somehow find myself in orbit and I need to fill up my tank how much would this run me? For simplicity's sake I'll assume I'm flying an RV. A rough estimate of the cost of material launched into orbit by a Soyuz spacecraft is about $12,500 per pound. A gallon of gas/diesel weighs in at 7.1 pounds making the cost of orbiting a gallon of gas about $88,750. Say the average price of a gallon of gas here in the US is $4.00 a gallon and we have gas prices of $355,00 per gallon. The average Winnebago as we know has an 80 gallon tank, so to fill said tank, I can expect to pay $28,400,000 at the pump according to my back of the envelope calculation.

Heak, I suppose if I was flying through space in an RV I'd be broke too.....

Pounds? Gallons? What are those...

EDIT:Sorry, I thought the reason the image wasn't showing was a combination of the USAF network and IE being fail. I fixed it now.

So they're still using liquid fuel? Isn't solid fuel comes easier on refueling, storage and less weight to deal with than liquid fuel? I suppose one pound of solid fuel out last one pound of liquid fuel.

Solid fuel has its own problems. Primarily, you can't use it to power multiple rockets at once. Solid fuel is essentially a one-way burn. So each thruster on a satellite would need its own solid fuel source... and that introduces balance problems if one depletes faster than the rest, altering the satellite's center of gravity. And, as in the name, it's basically a solid which makes refueling more difficult.

More significantly, once you start a solid going, it's going to keep going until it's depleted. Solid fuels do not allow precise control, or start/stop operation. That's why they're used for the main boost phase, since you want high efficiency, high thrust, and you want it to keep going as simply as possible (liquid fuel systems involve more parts, which means more things can go wrong) and as uniformly as possible. Once in orbit, you need precision and control, and that is provided by liquid fuel, not solids.

Hmmm. So lets say I somehow find myself in orbit and I need to fill up my tank how much would this run me? For simplicity's sake I'll assume I'm flying an RV. A rough estimate of the cost of material launched into orbit by a Soyuz spacecraft is about $12,500 per pound. A gallon of gas/diesel weighs in at 7.1 pounds making the cost of orbiting a gallon of gas about $88,750. Say the average price of a gallon of gas here in the US is $4.00 a gallon and we have gas prices of $355,00 per gallon. The average Winnebago as we know has an 80 gallon tank, so to fill said tank, I can expect to pay $28,400,000 at the pump according to my back of the envelope calculation.

Heak, I suppose if I was flying through space in an RV I'd be broke too.....

1 space buck = 1 million earth bucks. Also, avoid the special at the fuel depot.